I have a little demo example I often use to illustrate
(subdir test is not in classpath of program).

Arne

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import java.io.*;
import java.net.*;

public class DoubleDynmaic {
   private static void dynno(int n) {
      (new File("test")).mkdir();
      try {
         OutputStream os = new FileOutputStream("test/Test.java");
         PrintStream ps = new PrintStream(os);
         ps.println("public class Test {");
         ps.println("   public Test() {");
         ps.println("      System.out.println(" + n + ");");
         ps.println("   }");
         ps.println("}");
         ps.close();
         os.close();
         Runtime.getRuntime().exec("javac -d test
test/Test.java").waitFor();
         URL[] url = new URL[1];
         url[0] = new URL("file:test/");
         URLClassLoader cl = new URLClassLoader(url);
         Class.forName("Test", true, cl).newInstance();
      } catch (Exception e) {
         e.printStackTrace();
      }
   }
   public static void main(String[] args) {
      for(int i = 0; i < 10; i++) {
         dynno(i);
      }
   }
}